Impact Resistant Propeller System, Fast Response Electric Propulsion System And Lightweight Vertical Take-Off And Landing Aircraft Using Same

ABSTRACT

An aerial vehicle adapted for vertical takeoff and landing using pivoting thrust producing elements for takeoff and landing. An aerial vehicle which is adapted to takeoff with thrust units providing vertical thrust and then transitioning to a horizontal flight path. An aerial vehicle with pivoting thrust units with propellers, wherein some or all of the propellers are able to be stowed and fully nested during forward flight. An aerial vehicle adapted to withstand impacts upon its propellers. An aerial vehicle able to quickly alter the thrust of its propellers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/218,845 to Bevirt et al., filed Mar. 18, 2014, which ishereby incorporated by reference in its entirety.

BACKGROUND

1. Field of the Invention

This invention relates to powered flight, and more specifically to avertical take-off and flight control aircraft and flight method.

2. Description of Related Art

There are generally three types of vertical takeoff and landing (VTOL)configurations: wing type configurations having a fuselage withrotatable wings and engines or fixed wings with vectored thrust enginesfor vertical and horizontal translational flight; helicopter typeconfiguration having a fuselage with a rotor mounted above whichprovides lift and thrust; and ducted type configurations having afuselage with a ducted rotor system which provides translational flightas well as vertical takeoff and landing capabilities.

With VTOL aircraft, significantly more thrust may be required fortakeoff and landing operations than during regular forward flight. Thisextra thrust may also be required during the transitions betweenvertical and horizontal flight. In the case of propeller drivenaircraft, for example, with a plurality of pivoting thrust units usingpropellers for takeoff, some or many of these thrust units may be idledduring regular, horizontal forward flight.

What is called for is a thrust unit utilizing a propeller which allowsfor rotation of the thrust unit from a position of vertical thrust to aposition wherein the thrust unit provides horizontal thrust. What isalso called for is a thrust unit which is capable of stowing thepropeller blades completely, into a nested configuration.

SUMMARY

An aerial vehicle adapted for vertical takeoff and landing usingpivoting thrust producing elements for takeoff and landing. An aerialvehicle which is adapted to takeoff with thrust units providing verticalthrust and then transitioning to a horizontal flight path. An aerialvehicle with pivoting thrust units with propellers, wherein some or allof the propellers are able to be stowed and fully nested during forwardflight. An aerial vehicle adapted to withstand impacts upon itspropellers. An aerial vehicle able to quickly alter its thrust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an aerial vehicle in a takeoffconfiguration according to some embodiments of the present invention.

FIG. 2 is a perspective view of an aerial vehicle in a forward flightconfiguration according to some embodiments of the present invention.

FIG. 3 is a view of a stowing blade system in a deployed forward flightconfiguration according to some embodiments of the present invention.

FIG. 4 is a perspective view of a stowing blade system in a stowedconfiguration according to some embodiments of the present invention.

FIG. 5 is a front view of a stowing blade system in a stowedconfiguration according to some embodiments of the present invention.

FIG. 6 is a partial view of a stowing blade system in a stowedconfiguration according to some embodiments of the present invention.

FIG. 7 is a front partial view of a stowing blade system in a stowedforward flight configuration according to some embodiments of thepresent invention.

FIG. 8 is a partial view of a stowing blade system in a stowedconfiguration according to some embodiments of the present invention.

FIG. 8A is an illustration of a fin mount according to some embodimentsof the present invention.

FIG. 9 is a partial view of a stowing blade system in a stowedconfiguration according to some embodiments of the present invention.

FIG. 10 is a side view of an exemplary blade stowed according to someembodiments of the present invention.

FIG. 11 is a side view of an articulated mounting system in a forwardflight configuration according to some embodiments of the presentinvention.

FIG. 12 is a side view of an articulated mounting system in a take offconfiguration according to some embodiments of the present invention.

FIG. 13 is a side view of an articulated mounting system in atransitioning configuration according to some embodiments of the presentinvention.

FIG. 14 is a top view of an articulated mounting system in atransitioning configuration according to some embodiments of the presentinvention.

FIG. 15 is a perspective view of an articulated mounting system in atransitioning configuration according to some embodiments of the presentinvention.

FIG. 16 is a partial side view of an articulating mounting system withits blades deployed according to some embodiments of the presentinvention.

FIG. 17 is a rear perspective view of an articulated mounting systemaccording to some embodiments of the present invention.

FIG. 18 is a partial view of the underside of a rotor hub according tosome embodiments of the present invention.

FIG. 19 is a partial side cutaway view of the stowing mechanicsaccording to some embodiments of the present invention.

FIG. 20 is a bottom perspective view of the rotor stowing mechanicsaccording to some embodiments of the present invention.

FIG. 21 is a front view of propeller blade positions according to someembodiments of the present invention.

FIG. 22 is a side view of propeller blade positions according to someembodiments of the present invention.

FIG. 23 is a side partial view of aspects of a blade pivot systemaccording to some embodiments of the present invention.

FIG. 24 is a front view of stowed propeller blades according to someembodiments of the present invention.

FIG. 25 is a side view of stowed propeller blades according to someembodiments of the present invention.

FIG. 26 is a front perspective view of stowed propeller blades accordingto some embodiments of the present invention.

FIGS. 27A-C are views of a propeller system with different blade coningangles according to some embodiments of the present invention.

FIGS. 28A-F are illustrations of a blade strike according to someembodiments of the present invention.

FIG. 29 is a side view of a rotor deployment mechanism in a stowedconfiguration according to some embodiments of the present invention.

FIG. 30 is a side view of a rotor deployment mechanism in a deployedconfiguration according to some embodiments of the present invention.

FIGS. 31A-D illustrate views of an aerial vehicle from take-off totransition to forward flight according to some embodiments of thepresent invention.

DETAILED DESCRIPTION

Although vertical takeoff and landing (VTOL) aircraft have always beendesired, compromises in the realization of these aircraft have limitedtheir usefulness and adoption to certain niches. The thrust needed forVTOL is significantly higher than the thrust needed to maintainhorizontal flight. The vertical take-off thrust may also be neededduring the transition to forward flight. Once moving in forward flight,the wings of the aircraft provide lift, supplanting a function deliveredby motors during VTOL and during transition. Thrust producing elementsneeded during take-off, but not during forward flight, may be alteredduring forward flight such that they impart less drag onto the flyingsystem.

In some aspects, an aerial vehicle may use bladed propellers powered byelectric motors to provide thrust during take-off. The propeller/motorunits may be referred to as rotor assemblies. In some aspects, the motordriven propeller units on the wings may rotate relative to a fixed wing,such that the propellers provide vertical thrust for take-off andlanding. The rotation of the motor driven propeller units may allow fordirectional change of thrust by rotating both the propeller and theelectric motor, thus not requiring any gimbaling, or other method, oftorque drive around or through a rotating joint. The motor drivenpropeller units may be referred to herein as motor driven rotor units.

In some aspects, some or all of the wing mounted motor driven rotors areadapted to have the rotor blades fold back into a stowed positionwherein the blades nest in recesses in the adjoining nacelle body aftera transition to horizontal flight. The nested blades may result in asignificantly lower drag of the aerial vehicle, while also allowing asignificantly reduced power usage with only some of the rotors providingforward thrust.

In some aspects, extended nacelles with two coaxial propellers are usedsuch that one of the propellers is used during forward flight, andanother during vertical take-off and landing. The VTOL propeller may beadapted to nest its blades during forward flight. In some aspects, theextended nacelle may reside at the tip of a wing, or at the end of arear V-tail element. In some aspects, each of the coaxial propellers hasits own electric motor. In some aspects, the coaxial propellers aredriven by the same electric motor. In some aspects, the electric motorhas directional clutches such that one propeller is driven while themotor rotates in a first direction, and the other propeller is drivenwhile the motor rotates in a second direction.

In some aspects, the mass balance of the aerial vehicle may be alteredby movement of masses such as the battery mass. In some aspects, thebattery mass may be adjusted to retain balance when a different numberof occupants are supported. In some aspects, mass balance may beadjusted in automatic response to sensors within the aerial vehicle. Insome aspects, the battery mass may be distributed between a two or morebattery packs. The battery packs may be mounted such that their positionmay be changed during flight in response to changes in the balance ofthe aerial vehicle. In some aspects, the flight control system of theaerial vehicle may sense differential thrust requirements duringvertical take-off and landing, and may move the battery mass in order toachieve a more balanced thrust distribution across the rotor assemblies.In some aspects, the battery mass may be moved should there be a failureof a rotor assembly during transition or vertical take-off and landing,again to balance the thrust demands of the various remaining functioningrotors.

In some embodiments of the present invention, as seen in FIG. 1, anaerial vehicle 100 is seen in take off configuration. The aircraft body101 supports a left wing 102 and a right wing 103. Motor driven rotorunits 140 include propellers 107 which may stow and nest into thenacelle body 106. The aircraft body 101 extends rearward is alsoattached to raised rear stabilizers 104. The rear stabilizers have rearmotors 105 attached thereto. Portions of the rotor unit have beenomitted in FIG. 1 for illustrative clarity.

FIG. 1 illustrates the aerial vehicle 100 in a vertical take-off andlanding configuration such that the thrust of the rotors is directedupward. The propellers 107 have been rotated relative to the nacellebodies 106 using articulated linkages. In this vertical take-off andlanding configuration, the aerial vehicle 100 is able to utilize sixpropellers providing thrust in a vertical direction. The propellers 107are adapted to raise the vehicle 100. After the initial verticaltake-off, the vehicle transitions to forward horizontal flight. Thetransition is facilitated by the articulation of the propellers from avertical thrust configuration to positions off of vertical,transitioning to a horizontal thrust configuration. FIG. 3 isillustrative of the motor driven rotor unit in a powered forward flightconfiguration.

As the aerial vehicle 100 transitions to a forward, horizontal, flightconfiguration, the wings 102, 103 begin to provide lift. Once travelingin a horizontal attitude, with speed, significantly less thrust isneeded to propel the aerial vehicle 100 forward than was needed asvertical thrust during take-off. FIG. 2 illustrates a forward flightconfiguration of an aerial vehicle 100 wherein the blades 108 of thepropellers 107 have been stowed into recesses 110 on the nacelle bodies106. With the blades stowed during forward flight, a low drag profilemay be attained. In some aspects, some of the main propellers 107 may beused for forward flight. In some aspects, all of the main propellers 107may be stowed, and alternate forward flight propellers 111 may be usedin forward flight.

In an exemplary configuration of the first embodiment, the aerialvehicle has 6 rotors and weighs 900 kg. The rotor diameters are 2.1meters, with a thrust per rotor of 1500 N in hover. The continuous rpmof the motor at sea level is 1030 rpm, with a maximum of 1500 rpm. Thewingspan is 7.5 meters. The battery mass is 360 kg, and the mass permotor is 9 kg. The cruise speed is 320 km/h. The continuous hover shaftpower per motor is 25 kW at standard sea level conditions.

FIGS. 3 and 4 illustrate the deployed and stowed configurations,respectively, of the main propellers 107 of the motor driven rotor units140. In the deployed configuration, the propeller blades 108 of thepropeller 107 are deployed to a position approximately perpendicular tothe rotation axis of the motor driven rotor unit 140. The actual bladeangle may vary as a function of motor rpm and other factors, asdiscussed below. A spinner 109 presents a leading surface for the motordriven rotor unit 140.

In the stowed configuration, the blades 108 reside within recesses 110in the nacelle body 106. As seen in front view in FIG. 5, in the stowedconfiguration the outer surface of the forward portion of the nacelle iscomposed of the surfaces of the blades 108 of the propeller 107. Theouter surface of the nacelle with the blades in the stowed configurationis a composite of the five blades' surfaces. The blades and the nacellesmay be designed in concert such that the nacelle aerodynamicrequirements and those of the propeller fit into each other into acomplementary design. The recesses 110 may be adapted to provide a verysnug fit for the blades 108 in the stowed configuration.

FIGS. 6 and 7 illustrate a perspective view and a front view,respectively, of a motor driven rotor unit with the spinner removed tohelp the viewer visualize a design according to some aspects of thepresent invention. The main hub 122 is seen as a mounting point for eachof the five propeller blades 108. The main hub 122 provides the mainsupport of the propeller blades, which are each pivotally connected tothe main hub. The main hub 122 also provides the drive torque to theblades 108 of the propeller 107. As discussed further below, the mainhub 122 is coupled to the outboard bracket of the rotor deploymentmechanism via a rotary bearing, or bearing assembly.

FIG. 8 illustrates a perspective view of a motor driven rotor unit withfurther portions removed for clarity of illustration. The propellerblade 108 is illustrated solely as a partial blade 142, allowing forobservation of the fin mount 121. The fin mount 121 is bonded within the(missing in this view) inner portion of the propeller blade. In someaspects, the propeller blade is formed from a number of pre-formedpieces which are then bonded together, with the fin mount affixedtherein. The fin mount 121 may be metal, and constructed such that it isadapted to allow for mounting to the main hub 122 with a hinge pin 123,for example. In some embodiments, as seen in FIG. 8A, the fin mount 121may be a plurality of independent pieces. These pieces may be fixturedduring assembly of the propeller blade 108 such that the finishedcomponent is adapted to mount to the main hub 122 with a hinge pin. Astowing tab 143 may be affixed to the fin mount 121 to allow for movingthe blade into a stowed configuration into the recess and against thenacelle body. In some aspects, the propeller blade 108 may be of acomposite material. The propeller blade 108 may be assembled from piecessuch that the blade is a hollow shell assembled from pre-manufacturedindividual pieces. A deploy spring 141 allows for the blades of thepropeller to achieve a deployed configuration in the absence ofcentrifugal forces. The deploy spring allows for full deployment of thepropeller blades even when the rotors are not turning. To achieve fullstowage, the stowing tabs 143 on the propeller blades 108 of thepropeller 107 are pushed on by a stowing mechanism, until the blades arefit within the recesses 110 of the nacelle bodies.

FIG. 9 illustrates another perspective view of a motor driven rotor unitwith even further portions removed for clarity of illustration. The mainhub 122 is seen supporting the fin mount 121. The fin mount 121 isadapted to pivot relative to the main hub 122 using a hinge pin 123. Insome recesses, the partial blades 142 are seen, and other recesses 110no blade is seen, for purpose of visual clarity only. As the furtherportions have been removed for illustrative effect, the rotor deploymentmechanism, the motor, and other components come into view.

FIG. 10 illustrates a side view of portions of a rotor according to someembodiments of the present invention. The propeller blade 108 is seen ina stowed position. The propeller blade 108 is hinged with a hinge pin123 to the main hub 122. The main hub is seen mounted within a bearingassembly 125. The bearing assembly 125 is mounted to the outboardbracket 124 of the rotor deployment mechanism. In some aspects, the mainhub 122 is mounted to the inner race or races of the bearing assembly125, and the outer race of the bearing assembly 125 is mounted withinthe outboard bracket 124 of the rotor deployment mechanism.

FIG. 11 is a side view of portions of a rotor deployment mechanism of adeployable motor driven rotor assembly in a forward flight configurationaccording to some embodiments of the present invention. The mainmounting points 127, 128 are the structural attachment points for therotor deployment mechanism 143, and by extension, for the motor drivenrotor unit, to the aerial vehicle. The drive motor 126 is adapted todrive the rotor main hub 122, and by extension, the propeller of therotor unit. In this forward flight configuration, the rotor thrustvector is oriented forward with regard to the aerial vehicle, and ishorizontal.

FIG. 12 illustrates rotor deployment mechanism 143 in a deployed,vertical take-off, configuration. The rotor deployment mechanism hasboth rotated and displaced the rotor. The deployment has pushed therotor hub forward, and away, from the main mounting points 127, 128, aswell as upward vertically relative to the main mounting points. In thisvertical take-off configuration, the rotor axis is vertical. In someaspects, with the use of rotor deployment mechanisms as describedherein, the nacelle may be seen as being split during the rotordeployment such that the rear portion of the nacelle stays with the wingin a fixed positional relationship. The rotor deployment may then beable to occur from a nacelle along the wing, or along a rear horizontalstabilizer element. The rotor deployment mechanisms may be mounted at aposition that is not the end of the wing, or other horizontal element.

The outboard bracket 124 is attached to the deployment linkages at thebracket attach points 134, 135. The bracket arms 129, 130, 131 link viapivot points 132, 133. With the use of multi-arm linkages the rotor maybe moved to preferred positions in both the deployed and stowedconfigurations. FIGS. 13-16 illustrate the rotor with its linkages in apartially deployed configuration, which is seen during transitions fromvertical to horizontal thrusting, or from horizontal to verticalthrusting.

The electric motor/propeller combination being on the outboard side ofthe articulating joint allows for a rigid mounting of the propeller tothe motor, which is maintained even as the propeller is moved throughvarious attitudes relative to the rear nacelle portion. With such aconfiguration the rotating power from the motor need not be gimbaled orotherwise transferred across a rotating joint.

FIG. 17 illustrates a deployment drive system for a deployment mechanismaccording to some embodiments of the present invention. A drive unit 151may be coupled to the aerial vehicle, within the wing in an areaadjacent to the mounting points for the main mounting points 127, 128.Drive screws 150 may be driven such that the deployment linkage isdriven from a stowed configuration to a deployed configuration, and froma deployed configuration to a stowed configuration.

FIG. 18 is a partial view of the underside of a main rotor hub 122mounted into an outboard bracket 124 of a rotor deployment mechanismaccording to some embodiments of the present invention. A stowing rod153 is adapted to drive the stowing levers 152 against the stowing tabs143. The stowing tabs 143 then drive the propeller blades into a nestedposition onto the nacelle body. The deploy springs 141 are adapted todeploy the propeller blades 108 from a stowed position to a deployedposition. FIG. 19 is a partial side cutaway view of the stowing rod 153coupled to a plurality of stowing levers 152. The stowing rod 153 may bedriven by a linear actuator to engage the stowing tabs 143 in order todeploy the propeller blades from their stowed, nested, configuration.When fully deployed, the propeller blades will not reside on the stowinglevers. FIG. 20 is a bottom perspective view of the stowing rod 153 andits coupling to the stowing levers 152, and ultimately to the fin mounts121 of the propeller blades 108. Position indicators may be used toproperly line up the propeller relative to the recesses in the nacelle.

In an exemplary embodiment of a method for flying an aerial vehicle withan articulated electric propulsion system and fully stowing blades, anaerial vehicle may be on the ground. The aerial vehicle may have aplurality of wing and tail mounted motor driven rotor units. The motordriven rotor units may begin with propeller blades that are stowed suchthat the stowed propeller blades comprise all or most of the effectivewetted area of portions of the nacelles of which they form a part. Thenacelles may have recesses adapted to receive the stowed blades.

The stowed blades may be held in the stowed position with the assistanceof stowing mechanisms. In preparation for vertical take-off, the stowedblades may deploy to a deployed configuration. The blades may utilizedeployment springs which assist with the deployment of the blades uponthe release of stowing levers. The stowing levers may be adapted topivot the propeller blades from a deployed to a stowed configuration.

Once the propeller blades are in a deployed position, the entire motordriven rotor assembly may be itself deployed from a forward flightposition to a vertical take-off and landing position with the use of anarticulating rotor deployment mechanism. The deployment mechanism isadapted to position the propellers in front of and above the wings, orotherwise clear of other aerial vehicle structure. With the propellerblades now deployed, and with the motor driven rotor units nowarticulated into a vertical take-off configuration, the aerial vehicleis able to begin a vertical take-off. The rotors are spun up and thevehicle rises from the ground.

After take-off, the aerial vehicle will begin a transition to forwardflight by articulating the rotors from a vertical thrust orientation toa position which includes a horizontal thrust element. As the aerialvehicle begins to move forward with speed, lift will be generated by thewings, thus requiring less vertical thrust form the rotors. As therotors are articulated further towards the forward flight, horizontalthrust, configuration, the aerial vehicle gains more speed.

Once the aerial vehicle is engaged in regular forward flight, thepropellers in use during take-off may no longer be necessary. The thrustrequirement for forward flight may be significantly less than thatrequired during vertical take-off and landing. The forward flight may bemaintained by just a subset of the propellers used for take-off, or bydifferent propellers than those used during take-off. The unusedpropellers may have their propeller blades stowed in to recesses on thenacelles supporting the propellers. The stowed propeller blades may formthe exterior surface of portions of the nacelle.

In some embodiments of the present invention, as seen in FIGS. 21 and22, propeller blades 501 may be attached to a central hub 522 such thatas the blade pivots from a forward, deployed, position towards a stowedposition the blade counter-rotates relative to its normal rotationdirection 512. Using the multiple views shown in FIGS. 21 and 22 toillustrate the geometry, the views illustrate the same relative bladepositions. In a first position 501 a, 502 a, the blade is coned forwardrelative to the central hub 522. With this most forward coned position502 a as seen in FIG. 22, the blade is also rotationally at a mostforward position 501 a, as seen in FIG. 21. As the blade moves backwardsslightly 502 b relative to the most forward position 501 a, the bladealso retards angularly relative to the central hub to a slightlyretarded position 501 b.

As the blade moves further backwards, relative to the forward conedposition, through more positions 502 c, 502 d, the blade issimultaneously moving back through a series of angularly retardedpositions 501 c, 501 d.

Among the advantages of this system is that should a blade be struck byan object, such as a bird, during flight, the system acts in a coupledfashion to lower the impact forces. As the strike hits the blade fromthe front, the blade is pushed back. The inertia of the impactingobject, through its inertia, imparts a force on the blade in an angulardirection counter to its undisturbed helical direction of motion.Through the coupling of the system, as the impact causes the blade topivot backwards relative to a more forward coned position, the couplingretards the blade along its spin direction in such a way that it movesroughly in the direction of the motion of the impacting object, thusmoderating the impact upon the blade. Not only is the strain reduced,but the impact shock loading will also be reduced.

The coning angle is achieved as a result of the balance between theaerodynamic and inertial moments generated by the blades. By angling theblade pivot axis relative to a plane normal to the propeller rotationalaxis, the blade may be made to retard relative to the rotational axis asit is pushed backwards with regard to cone angle. The pivot assembly 523may have two bores 524, 525. The axis of a first bore 524 closest to theblade 501 may be pushed forward along the spin axis relative to the axisof a second bore 525. This staggering of the bores 524, 525 along adirection parallel to the rotational axis of the propeller and itscentral hub 522 will allow for the angular retardation of the blade asthe blade is pushed backwards from a forward coning angle. When theblade pivot axis is angled as discussed above, the coupled system allowsan impacted blade to both slow down and flap backward during the impact,dramatically reducing the impact loads on the blade, the hub, and thesupport structure.

In some embodiments, in order to help achieve a well nested set ofstowed blades which also have good figure of merit, the blades 501 mayhave some or significant forward sweep. Also, the pivot assembly 523 maybe canted in another angle in order to better the nested fit of the setof propeller blades. FIGS. 24, 25, and 26 illustrate front, side, andperspective views, respectively, of a propeller 508 with its blades 501in a stowed configuration. The outer surfaces of the stowed blades 501form almost a continuous surface. When stowed over an exterior surfaceof a nacelle with mating recesses, a very low drag stowed system can bemaintained.

FIGS. 28A-F illustrate a series of freeze frames of a rotating propeller508 being struck by a mass 516. The views illustrate the coupling, asboth front and side views are shown from the same moment in time, as theimpact affects the system. In these Figures, the propeller is spinningin a clockwise direction 515, with a very forward swept propeller blade.By the later timing in the timed sequence of FIG. 28D, the rotationalretardation of the impacted blade can be seen. Also, the downwarddeflection of the blade can be seen in the side view. By the timedsequence of FIG. 28E, the rotational retardation of the impacted bladecan be more clearly seen. Also, the downward deflection of the blade canbe more clearly seen in the side view. This sequence illustrates adistinct advantage of this coupled system.

FIGS. 27A-C illustrate top and side views of motor driven rotor assemblyaccording to some embodiments of the present invention. FIG. 27Aillustrates a motor driven rotor assembly wherein the propeller is conedbackwards somewhat. FIG. 27B illustrates a configuration wherein thepropeller blades are substantially perpendicular to the rotational axis.FIG. 27C illustrates a configuration wherein the propeller blades areconed forward.

As mentioned above, the coning angle is achieved as a result of thebalance between the aerodynamic and inertial moments on that propellerblade about its hinge axis. FIG. 27C is illustrative of a coning anglewhich may be seen during normal flight, whether forward flight orvertical take-off and landing. The blades 532 cone up at an angle 530relative to a plane 531 normal to the spin axis of the propeller. Shouldthere be an increase in the rotational speed of the propeller blade,such as may be desired or required during flight, or duringtake-off/landing, the resultant increased centrifugal force on theblades, will flatten the blades relative to the initial forward coningangle 530. The resulting position may be as seen if FIG. 27B. The blades533 are now seen in plane with the normal 531 to the spin axis, althoughany angle that is closer to normal than the initial forward coning angle530 may result, depending upon flight parameters and circumstances.

In some embodiments, with the angling of the blade pivot axis asdiscussed above, the blade pitch will increase as the blade pivots froma more forward coning angle to a flatter coning angle. This change inpitch results as a function of system geometry with the angled pivot pinsystem.

With the use of electric motors as part of the motor driven rotorassemblies, this system will have an advantage in that very quickresponses in thrust are achievable. The electric motors are able todeliver changes in torque very quickly relative to internal combustionengines, or jet engines, for example. An application of increased torqueto the propeller hub will result in an initial lag motion of the bladesdue to their inertia, and this lag motion will result in a change ofpitch of the blades. Thus, while the motor is accelerating the pitch ofthe blades increases. This system, which uses quick to respond electricmotors, and also uses a propeller blade system which increases pitchangle with a lag motion of the propeller blades, allows for previouslyunseen responsiveness in a flight system.

FIG. 29 is a side view of portions of a rotor deployment mechanism of adeployable motor driven rotor assembly in a forward flight configurationaccording to some embodiments of the present invention. The mainmounting points 541, 542 are the structural attachment points for therotor deployment mechanism 540, and by extension, for the motor drivenrotor unit, to the aerial vehicle. The drive motor 543 is adapted todrive the rotor main hub 522, and by extension, the propeller of therotor unit. In this forward flight configuration, the rotor thrustvector is oriented forward with regard to the aerial vehicle, and ishorizontal.

FIG. 30 illustrates rotor deployment mechanism 540 in a deployed,vertical take-off, configuration. The rotor deployment mechanism hasboth rotated and displaced the rotor. The deployment has pushed therotor hub 522 forward, and away, from the main mounting points 541, 542,as well as upward vertically relative to the main mounting points. Inthis vertical take-off configuration, the rotor axis is vertical. Insome aspects, with the use of rotor deployment mechanisms as describedherein, the nacelle may be seen as being split during the rotordeployment such that the rear portion of the nacelle stays with the wingin a fixed positional relationship. The rotor deployment may then beable to occur from a nacelle along the wing, or along a rear horizontalstabilizer element. The rotor deployment mechanisms may be mounted at aposition that is not the end of the wing, or other horizontal element.

The outboard bracket 544 is attached to the deployment linkages at thebracket attach points 134, 135. The bracket arms link via pivot points.With the use of multi-arm linkages the propeller may be moved topreferred positions in both the deployed and stowed configurations.

The electric motor/propeller combination being on the outboard side ofthe articulating joint allows for a rigid mounting of the propeller tothe motor, which is maintained even as the propeller is moved throughvarious attitudes relative to the rear nacelle portion. With such aconfiguration the rotating power from the motor need not be gimbaled orotherwise transferred across a rotating joint. The deployment is of theentire motor driven rotor in some aspects.

FIGS. 31A-D illustrate an aerial vehicle 600 during take-off and throughtransition to forward flight according to some embodiments of thepresent invention. In this illustrative embodiment, the aerial vehicle600 has a body 601, wings 602, 603, and a tail structure 604. The motordriven rotor assemblies 605 along the midspan of the wing, and attachedto the tail structure, have articulating mechanisms adapted to deploythe rotor assemblies. This allows for vertical thrust for take-off andlanding, as seen in FIG. 31A. The wing tip rotor assemblies 606 areadapted to pivot to a vertical thrust orientation as well.

After take-off, the rotor assemblies 605, 606 are adapted to transitiontowards a forward flight configuration, with the thrust moving from avertical orientation towards a horizontal orientation, via motion of therotor assemblies, as seen in FIG. 31B. At transition to forward flight,as seen in FIG. 31C, the rotor assemblies 605, 606 have fullytransitioned to a horizontal thrust position.

With the lift provided by the wings 602, 603, supporting the aerialvehicle 600, less thrust is needed to keep the vehicle flyinghorizontally. In order to save power and to reduce drag, the blades 605of the mid span mounted and rear stabilizer mounted rotor assemblies 605may have their blades nested against the nacelles. The reduced dragforward flight configuration is illustrated in FIG. 31D.

Nested blades according to some embodiments of the present inventionprovide a very large decrease in drag. For example, in an illustrativecase, feathering blades on an unused motor driven propeller assemblywould result in 128N of drag. Simple folding of the blades results in105N of drag. Yet with nested blades the drag is reduced to 10N. Thiscompares very favorably to a bare nacelle, with 7N of drag.

In some aspects, the blades of the mid span mounted and rear stabilizermounted rotor assemblies 605 are pivotally attached to a rotor hub. Theblades 612 of these rotor assemblies may be forward swept, and attachedusing an angled pin mechanism as described above. These blades may stowinto recesses in the nacelles. The wing tip mounted rotor assemblies 606may have blades 613 which are variable pitch blades. These blades maypower the vehicle during forward flight.

The wing tip mounted blades 613 may rotate in a direction opposite theinner blades along the wing. In addition, the wing tip mounted propellermay rotate such that it counters the tip vortexes of the wings. The wingtip mounted rotor will rotate such that the blades are coming downward610, 611 exterior to the wings. Thus, the left side wing tip propellerand the right side wing tip propeller will rotate in differentdirections.

As evident from the above description, a wide variety of embodiments maybe configured from the description given herein and additionaladvantages and modifications will readily occur to those skilled in theart. The invention in its broader aspects is, therefore, not limited tothe specific details and illustrative examples shown and described.Accordingly, departures from such details may be made without departingfrom the spirit or scope of the applicant's general invention.

What is claimed is:
 1. An impact resistant propeller system, said impactresistant propeller system comprising: a propeller, said propellerhaving a primary spin direction along a first spin axis to providepositive thrust, said propeller comprising: a central hub, said centralhub comprising a first rotation axis; a plurality of propeller blades,each of said plurality of propeller blades pivotally attached along afirst pivot axis to said central hub, wherein the first pivot axis isangled such that pivoting a propeller blade backwards along said firstspin axis causes the propeller blade to rotate counter to said primaryspin direction.
 2. The impact resistant propeller system of claim 1wherein said first pivot axis is angled to a plane normal to the firstspin axis.
 3. The impact resistant propeller system of claim 2 whereinsaid propeller blades comprise a pivot pin, said pivot pin extendingfrom a leading edge of said propeller blade.
 4. The impact resistantpropeller system of claim 3 wherein said pivot pin comprises a first endat the leading edge of said propeller blade and a second end away fromsaid leading edge of said propeller blade, and wherein said first end isforward of said second end along said first spin axis.
 5. The impactresistant propeller system of claim 4 wherein said propeller systemfurther comprises a nacelle, and wherein said blades are adapted topivot from a deployed configuration substantially perpendicular to saidspin axis to a stowed position along the exterior of said nacelle. 6.The impact resistant propeller system of claim 5 wherein said nacellecomprises recesses around its exterior, and wherein said blades residein said recesses when in said stowed position.
 7. The impact resistantpropeller system of claim 6 further comprising a stowing mechanism, saidstowing mechanism adapted to stow said propeller blades into saidrecesses in the outer surface of the nacelle.
 8. The impact resistantsystem of claim 7 further comprising a spring system adapted to deploythe propeller blades from their stowed position.
 9. The impact resistantpropeller system of claim 8 further comprising a propeller deploymentmechanism, said propeller deployment mechanism adapted to deploy saidcentral hub from a first position wherein said first spin axis ishorizontal to a second position wherein said first spin axis isvertical.
 10. A quick response propeller system for an aerial vehicle,said system comprising: a central hub; a plurality of propeller blades,each of said plurality of propeller blades pivotally attached along afirst pivot axis to said central hub, wherein the first pivot axis isangled such that pivoting a propeller blade backwards along said firstspin axis from a position forward of normal to the spin axis causes achange in pitch of the propeller blade.
 11. The quick response propellersystem of claim 10 further comprising an electric motor coupled to saidcentral hub.
 12. The quick response propeller system of claim 11 whereinsaid first pivot axis is angled to a plane normal to the first spinaxis.
 13. The quick response propeller system of claim 12 wherein saidpropeller blades comprise a pivot pin, said pivot pin extending from aleading edge of said propeller blade.
 14. The quick response propellersystem of claim 3 wherein said pivot pin comprises a first end at theleading edge of said propeller blade and a second end away from saidleading edge of said propeller blade, and wherein said first end isforward of said second end along said first spin axis.
 15. An aerialvehicle adapted for vertical take-off and horizontal flight, said aerialvehicle comprising: a main vehicle body; a right side wing; one or moreright side rotor assemblies comprising propellers, wherein one or moreright side wing rotor assemblies are attached to said right side wing,and wherein said one or more right side wing rotor assemblies protrudeforward of the leading edge of said right side wing along a middlesection of the wing span, and wherein the propeller blades are adaptedto pivot from a stowed position in the recesses of the nacelle body to adeployed position substantially perpendicular to said stowed position;and a left side wing; one or more left side rotor assemblies comprisingpropellers, wherein one or more left side wing rotor assemblies areattached to said left side wing, and wherein said one or more left sidewing rotor assemblies protrude forward of the leading edge of said leftside wing along a middle section of the wing span, and wherein saidpropeller blades are adapted to pivot from a stowed position in therecesses of the nacelle body to a deployed position substantiallyperpendicular to said stowed position; a right side wing tip rotor unit,said right side wing tip rotor unit comprising a variable pitchpropeller; and a left side wing tip rotor unit, said left side wing tiprotor unit comprising a variable pitch propeller.
 16. The aerial vehicleof claim 15 wherein said right side wing rotor assemblies are attachedto said right wing by a deployment mechanism adapted to deploy saidright side wing rotor assemblies from a forward facing horizontal flightconfiguration to a vertical take-off configuration, and wherein saidleft side wing rotor assemblies are attached to said left wing by adeployment mechanism adapted to deploy said left wing rotor assembliesfrom a forward facing horizontal flight configuration to a verticaltake-off configuration.